Gasket flow sensing apparatus and method

ABSTRACT

An improved fluid flow sensor for measuring changes in temperatures of fluids flowing through apertures of a multiple-layered gasket is embedded between layers of the gasket. A thermal resistor type of sensor based upon hotwire anemometer technology in a preferred embodiment is responsive to changes in fluid temperature and flow velocity. A primary resistance with external current leads and separate auxiliary leads for voltage sensing are employed, wherein changes in resistance are virtually linearly proportional to changes in temperature. A four-point probe measurement method provides a most accurate reading of the temperature data to the extent that resistance associated with lead and contact resistances are minimized. The thermal resistor sensor is constructed of relatively thin layers of dielectric and electrically conducting materials having a low thermal mass, wherein the dielectric layers serve as support and electrical insulation to protect the sensor from environmental deterioration.

This application claims priority from U.S. Provisional PatentApplication No. 60/297,701, filed on Jun. 12, 2001, the contents ofwhich are incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates generally to flow rate sensing apparatus,and particularly to micro-fluidic methods applied to cylinder headgaskets for internal combustion engines. More specifically, theinvention relates to apparatus and methods for measuring temperatures offluids passing through apertures of cylinder head gaskets.

2. Description of the Prior Art

It is known to employ electronic sensors in cylinder head gaskets forsealing between engine components including, for example, the block andcylinder head of a multi-cylinder internal combustion engine. In onecase, the gasket comprises a sealing plate having several combustionchamber orifices, and combustion chamber sealing elements at the edgesof the sealing plate surrounding the combustion chamber orifices. Thegasket includes sensor elements for cylinder-specific detection ofsealing movements perpendicular to the plane of the sealing plate,caused by pressure changes in respective combustion chambers beingmeasured. All of the sensor elements are arranged outside of thecombustion chamber sealing elements and can be piezoelectric andpiezoresistive, as well as glass fiber lightguide-style sensors.

In another example, a gasket enclosed sensor system is employed formeasurement of combustion chamber parameters and delivery of signals topoints external of the engine. The gasket includes a combustion openingsubstantially surrounding a combustion chamber, and includes an accessopening extending from the combustion chamber to a point external of theengine. A metallic sensor terminal is positioned within the accessopening, and insulating material substantially surrounds the metallicsensor terminal.

In yet another example, an oil flow sensor and associated circuitry areused to indicate presence of oil flow in a multi-cylinder internalcombustion engine. The oil sensor includes a heating element positionedwithin the oil line, directly in the oil flow path. A comparatormeasures the value of signals from upstream and downstream heat sensors,and triggers a switching circuit when the temperature at the sensorsapproach one another to indicate an adequate oil flow to the engine. Thedisclosed oil flow sensor, however, is not associated with a combustionchamber gasket environment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an electric circuit of a Constant Current Anemometer(CCA) as designed in accordance with the present invention.

FIG. 2 illustrates an electric circuit of a Constant TemperatureAnemometer (CTA) as designed in accordance with the present invention.

FIG. 3 is an output diagram relating to FIG. 1 and FIG. 2.

FIG. 4 are two diagrams that illustrate a Constant Current Anemometer(CCA) wire dynamic response to Step change in velocity or Sinusoidalvelocity variation.

FIG. 5 is a diagram that illustrates Constant Temperature Anemometer(CTA) related amplitude transfer functions for velocity fluctuations.

FIG. 6 is a diagram that illustrates a “SQUARE WAVE TEST” result byusing an indirect method where the sensor is subjected to an electricsine wave that simulates an instantaneous change in velocity.

FIG. 7 illustrates an electric circuit to measure the ambienttemperature and/or flow velocity relating to FIG. 6.

FIG. 8 illustrates a thermal resistor consisting of a main resistancewith external leads and auxiliary leads for voltage sensing.

FIG. 9 is a plan view of one described embodiment of a fluid probe orfluid flow rate sensor of a fluid flow thermal transducer system of thepresent invention, shown positioned at the edge of a fluid aperture.

FIG. 10 is a plan view of an alternate embodiment of a fluid flowthermal transducer system as constructed in accordance with the presentinvention, shown in a conventional cylinder combustion gasket of aninternal combustion engine.

FIG. 11 is a plan view of a similar embodiment of a fluid flowtransducer of the type depicted in FIG. 10, shown in a test fixture tosimulate the fluid flow transducer system required for a conventionalcylinder combustion gasket for an internal combustion engine.

FIG. 12 is a series of sequential views of a micro-fluidic transducersystem during steps of manufacture, as prepared for the embodiment ofthe test fixture shown in FIG. 11.

FIG. 13 illustrates a schematic of a test fixture designed for atemperature sensitivity test of a microfilm sample sensor betweentemperature and voltage.

FIG. 14 is a diagram of results illustrating the limitation of appliedcurrent obtained from the test fixture in FIG. 13.

FIGS. 15 a and 15 b are diagrams that illustrate results obtainedthrough experiments utilizing the test fixture of FIG. 13 showing thatthe voltage values are linearly proportional to the water temperature.

FIG. 16 illustrates an electric circuit designed to measure flowvelocity.

FIG. 17 illustrates a schematic for a method of obtaining a flowvelocity measurement by measuring the voltage drop across a probesensor.

FIG. 18 illustrates a schematic of a test fixture designed to measureflow velocity as illustrated in FIG. 17 in order to obtain thesensitivity of a sample flow sensor.

FIG. 19 is a diagram that illustrates the test results of FIG. 18showing current vs. resistance where current is 0 to 5 mA.

FIG. 20 is a diagram that illustrates the test results of FIG. 18showing current vs. resistance where current is 5 to 10 mA.

FIG. 21 is a diagram that illustrates Test I results of FIG. 18 whereflow rate vs. voltage drop are measured where current is 5 mA.

FIG. 22 is a diagram that illustrates Test II results of FIG. 18 whereflow rate vs. voltage drop are measured where current is 5 mA.

FIG. 23 is a diagram that illustrates Test III results of FIG. 18 whereflow rate vs. voltage drop are measured where current is 10 mA.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides an improved flow sensor for an automotivegasket. The flow sensor is designed to be embedded between layers of amultiple-layered combustion sealing gasket, typically including layersof metallic material such as steel, and is particularly effective tomeasure changes in temperatures of coolants or oil flowing throughapertures of the gasket. The gasket of the disclosed embodiments issubjected to a range of temperatures including environmental ambienttemperature and an elevated operational temperature such as that whichtakes place in an internal combustion engine.

Theoretical Considerations

Governing Equations of Hot-Wire (Film) Anemometry Application

1) Governing equation: $\frac{\mathbb{d}E}{\mathbb{d}t} = {W - H}$

where, E=thermal energy stored in wireE _(w) =C _(w) ·T _(s)

Cw=heat capacity of wire

W=power generated by joule heatingW=i ² ·R _(w)

R_(w)=f(T_(w))

H=heat transferred to surroundings

For equilibrium conditions the heat storage is zero: W=H and the Jouleheating W equals the convective heat transfer H.

Here, H=Σ (convection to fluid+conduction to supports+radiation tosurroundings) where,

-   -   Convection: Q_(c)=Nu·A·(T_(w)−T_(a))        -   Nu=h·d/k_(f)=f (Re, Pr, M, Gr, α)        -   Re=ρ·U/μ    -   Conduction: f (T_(w), l_(w), k_(w), T_(supports))    -   Radiation: f(T _(w) ⁴−T_(f) ⁴)        In here, basic assumptions are

-   Radiation losses small

-   Conduction to wire supports small

-   T_(w) uniform over length of sensor

-   Velocity impinges normally on wire, and is uniform over its entire    length, and also small compared to sonic speed.

-   Fluid temperature (?) and density constant    2) Static Heat Transfer:    W=H→I ² ·R _(w) =h·A·(T _(w) −T _(a))→I ² R _(w)=(Nu k _(f) /d)A(T    _(w) −T _(a))

h=film coefficient of heat transfer

A=heat transfer area

d=wire diameter

k_(f)=heat conductivity of fluid

Nu=dimensionless heat transfer coefficient

Forced convection regime, i.e. Re>Gr^(1/3) (0.02 in air) and Re<140→Nu=A ₁ +B ₁ ·Re ^(n) =A ₂ +B ₂ ·UI ² R _(w) ² =E _(w) ²=(T _(w) −T _(a))(A+B·U ^(n)) “King's law”The voltage drop is used as a measure of velocity or temperature.3) The Resistance of Sensor Element is$R_{0} = \frac{1}{A_{w}\sigma_{0}}$Wire resistance can be written as: R_(w)=R_(o)[1+α_(o)(T_(w)−T_(o))]

R_(w)=wire hot resistance

R_(o)=wire resistance at T_(o)

α_(o)=temperature coefficient of resistance (TCR)

σ_(o)=thermal conductivity

ρ_(o)=thermal resistivity(1/σ_(o))

T_(w)=wire temperature

T_(o)=reference temperature

Define: “OVERHEAT RATIO” as: a=R_(w)/R_(a)

The voltage across wire is given by: E_(w) ²=I²R_(w)²=R_(w)(R_(w)−R_(a))(A₁+B₁U^(n)) or as R_(w) is kept constant by theservoloop: E_(w)=A+BU^(n)

4) Velocity and Temperature Sensitivity

E _(w) ² /R _(w) =I ² R _(w)=(R _(w) −R _(a))(A ₁ +B ₁ U ^(n))${E = {\frac{R_{1} + R_{L} + R_{w}}{R_{w}}E_{w}}},{\frac{E^{2}R_{w}}{\left( {R_{1} + R_{L} + R_{w}} \right)^{2}} = {\left( {A + {BU}^{n}} \right)\left( {T_{w} - T_{a}} \right)}}$CT mode: e_(w)=S₇₄θ+S_(u)u (e_(w)=fluctuating voltage signal)$\begin{matrix}{S_{u} = {\frac{\partial E_{w}}{\partial U} = {\frac{{nBU}^{n - 1}}{2}\left\lbrack \frac{R_{w}\left( {T_{w} - T_{a}} \right)}{A + {BU}^{n}} \right\rbrack}^{1/2}}} \\{S_{\theta} = {\frac{\partial E_{w}}{\partial\Theta} = {- {\frac{1}{2}\left\lbrack \frac{R_{w}\left( {A + {BU}^{n}} \right)}{T_{w} - T_{a}} \right\rbrack}^{1/2}}}}\end{matrix}$CC mode: e_(w)=S_(θ,cc)θ+S_(u,cc)u $\begin{matrix}{S_{u,{cc}} = {\frac{\partial E_{w}}{\partial U} = {{- \frac{\left( {{\overset{\_}{R}}_{w} - {\overset{\_}{R}}_{a}} \right)^{2}{nB}\quad{\overset{\_}{U}}^{n - 1}}{I\quad{\overset{\_}{R}}_{a}}} = {- \frac{{nB}\quad{\overset{\_}{U}}^{n - 1}I^{3}{\overset{\_}{R}}_{w}^{2}}{{R_{a}\left( {A + {B\quad{\overset{\_}{U}}^{n}}} \right)}^{2}}}}}} \\{S_{\theta,{cc}} = {\frac{\partial E_{w}}{\partial\Theta} = \frac{\alpha_{0}I\quad{\overset{\_}{R}}_{w}R_{0}}{{\overset{\_}{R}}_{a}}}}\end{matrix}$Modes of Anemometer Operation

1) Constant current anemometer (CCA)—FIG. 1.

-   Principle: Current through sensor is kept constant-   Advantages:—High frequency response-   Disadvantages:—Difficult to use    -   Output decreases with velocity    -   Risk of probe burnout        $\frac{R_{w} + R_{L}}{R_{1}} = \frac{R_{3}}{R_{2}}$

2) Constant Temperature Anemometer (CTA)—FIG. 2.

Principle: Sensor resistance is kept constant by servo amplifierAdvantages: Easy to use High frequency response Low noise Acceptedstandard Disadvantages: More complex circuit

3) Note following comments to CTA and to CCA—FIG. 3:

-   -   Response is non-linear:        -   CCA output decreases        -   CTA output increases            In CTA mode, sensitivity decreases with increasing U

4) Non-Isothermal Condition with CT Mode

For accurate velocity measurements, a hot-wire probe is usually operatedat a high overheat ratio, making the ratio of the velocity sensitivityto the temperature sensitivity large. On most of the recent experimentalmethods, the smaller temperature term in equation is treated as acorrection term, with the fluctuating temperature, measuredindependently by the resistive-wire (or Cold-wire) method. S_(θ)=S_(θ,s)H_(p)′ where, H_(p)′ is the lower than unity and it is the plateau levelof the transfer function, H_(θ)(f).

The measurement of θ is usually carried out with a thin resistive-wireoperated in the CC mode, and the following relationship applies for themeasured temperature fluctuation, θ_(m)=H_(p)θ. Here, H_(p) is theplateau level of the amplitude transfer function for the temperaturefluctuations of the resistance-wire.e _(w) =S _(u) u+S _(θ) θ=S _(u) u+S _(θ,s)(H _(p) ′/H _(p))θwhere $\begin{matrix}{S_{u} = {\frac{\partial E_{w}}{\partial U} = {\frac{{nBU}^{n - 1}}{2}\left\lbrack \frac{R_{w}\left( {T_{w} - T_{a}} \right)}{A + {BU}^{n}} \right\rbrack}^{1/2}}} \\{S_{\theta} = {\frac{\partial E_{w}}{\partial\Theta} = {- {\frac{1}{2}\left\lbrack \frac{R_{w}\left( {A + {BU}^{n}} \right)}{T_{w} - T_{a}} \right\rbrack}^{1/2}}}}\end{matrix}$5) Sensitivity Evaluation of Copper Film

The resistance of sensor element is$R_{0} = {\frac{l}{A_{w}\sigma_{0}} = {21.5\quad\Omega}}$

-   -   where, length (l)=25 mm    -   width (w)=10 μm    -   thickness (t)=2 μm    -   A_(w)=w×t    -   ρ_(o)=1.72 μΩm    -   σ_(o)=5.8 e+7 (1/Ωm)    -   α_(o)=3,900 ppm/° C.        Wire resistance can be written as:        R_(w)=R_(o)[1+α_(o)(T_(w)−T_(o))]        In constant current mode (I=1 mA), the equation will be        rewritten as        IR _(w) =IR _(o)[1+α_(o)(T _(w) −T _(o))]=V _(w) =V        _(o)[1+α_(o)(T _(w) −T _(o))]=V _(o)+α_(o) V _(o)(T _(w) −T        _(o))        In case of unit overheat ratio (a≈1), temperature sensitivity of        sensor considered can be expressed as        $S_{\theta,{cc}} = {\frac{\partial E_{w}}{\partial\Theta} = {{\frac{\alpha_{0}I\quad{\overset{\_}{R}}_{w}R_{0}}{{\overset{\_}{R}}_{a}} \approx {\alpha_{0}{IR}_{0}}} = {83.85\quad\left( {µ\quad V\text{/}^{\quad{^\circ}}{C.}}\quad \right)}}}$        Dynamic Response

1) Constant Current Anemometer (CCA)

For analysis of wire dynamic response, governing equation includes theterm due to thermal energy storage within the wire:W=H+dE/dtThe equation then becomes a differential equation:I ² R _(w)=(R _(w) −R _(a))(A+BU ^(n))+C _(w)(dT _(w) /dt) or expressingT_(w) in terms of R_(w):I ² R _(w)=(R _(w) −R _(a))(A+BU ^(n))+C _(w)/α_(o) R _(o)(dR _(w) /dt)C _(w)=heat capacity of the wire(ρ_(w) c _(w)(π/4)d²1)α_(o)=temperature coefficient of resistance (TCR) of the wireThe first-order differential equation is${{\frac{C_{w}}{\alpha_{0}{R_{0}\left( {A + {BU}^{n} - I^{2}} \right)}}\frac{\mathbb{d}R_{w}}{\mathbb{d}t}} + R_{w}} = {\frac{\left( {A + {BU}^{n}} \right)}{\left( {A + {BU}^{n} - I^{2}} \right)}R_{a}}$And also can be characterized by a single time constant τ(=M):$\begin{matrix}{M = {\frac{C_{w}}{\alpha_{0}{R_{0}\left( {A + {BU}^{n} - I^{2}} \right)}} = \frac{C_{w}\left( {R_{w} - R_{a}} \right)}{\alpha_{0}R_{0}I^{2}R_{a}}}} \\{= {{\left\{ \frac{c_{w}\rho_{w}}{\chi_{0}\alpha_{0}} \right\}\left\lbrack {\frac{\pi}{4}\mathbb{d}^{2}} \right\rbrack}^{2}\left\{ \frac{\left( {{R_{w}/R_{a}} - 1} \right)}{I^{2}} \right\}}}\end{matrix}$The normalized transfer function can be expressed as:H_(wire)(ω))=(1+ω²M²)^(−1/2) where, ω is the angular frequency. When orω=1/M, the amplitude is reduced by −3 dB (or a factor of 1/1.414) andthe corresponding phase lag is −45°.Frequency limit can be calculated from the time constant:f_(cp)=1/(2πM).Frequency response of film-probes is mainly determined by the thermalproperties of the backing material (substrate).The time constant for film-probes becomes:M=τ=(R/R₀)²F²r_(s)C_(s)k_(s)/(A+BU^(n))²

-   -   r_(s)=substrate density    -   C_(s)=substrate heat capacity    -   k_(s)=substrate heat conductivity        and the normalized transfer function becomes:        H_(film)(f)=1/(1+(jf/f_(cp))^(0.5))        Dynamic characteristic may be described by the response to Step        change in velocity or Sinusoidal velocity variation as shown in        FIG. 4.

2) Constant Temperature Anemometer (CTA)—FIG. 5.

CTA keeps the wire at constant temperature hence the effect of thermalinertia is greatly reduced. One method to determine the dynamic responseof the anemometer is to apply the electronic disturbance signal, e_(t),to the anemometer. The electronic testing may take the form of either asquare-wave or sine-wave test. Through the many theoretical andexperimental works, a second order system approach may be useful toillustrate the effect of system damping. The related equation for thefluctuating bridge voltage e can be expressed as${\frac{\mathbb{d}^{2}e}{\mathbb{d}t^{2}} + {2\quad \quad\omega_{0}\frac{\mathbb{d}e}{\mathbb{d}t}} + {\omega_{0}^{2}e}} = {\omega_{0}^{2}\left\{ {{S_{u}u} + {S_{t}\left\lbrack {{M\frac{\mathbb{d}e_{t}}{\mathbb{d}t}} + \left( {1 + {\frac{2{{\overset{\_}{R}}_{w}\left( {{\overset{\_}{R}}_{w} - R_{a}} \right)}}{R_{a}\left( {{\overset{\_}{R}}_{w} + R_{1}} \right)}e_{t}}} \right)} \right\rbrack}} \right\}}$where ω₀ is the natural frequency of electronic circuit, ζ is thedamping coefficient, and Su and St are the sensitivity coefficients ofthe velocity and electronic test signals. Assuming that the wire had anoverheat ratio, R_(w)/R_(a), of 1.5, the sensor had a time constant, M,of 0.4 ms, the amplifier had a time constant 25 μs and that the value ofthe system gain parameter was 1250, the natural frequency f₀=(½π)w₀ as55 kHz, FIG. 5 shows the related amplitude transfer functions forvelocity fluctuations for values of ζ equal to 0.1, 1 and 10. Theoptimum response is seen to correspond to critical damping conditions(ζ≈1). An increase in velocity usually results in an increase in thefrequency response and a decrease in the value of the dampingcoefficients.

The time constant can be reduced toτ_(CTA)=τ_(CCA)/(2a S R _(w))where α=overheat ratio

-   -   S=amplifier gain    -   R_(w)=hot wire resistance        Frequency limit: fc defined as −3 dB amplitude damping.        3) Dynamic Calibration Methods—FIG. 6.        Direct Method

For the direct method to be used, it is necessary to have a flow inwhich sinusoidal velocity variations of known amplitude are superimposedon a constant mean velocity

-   -   Microwave simulation of turbulence (<500 Hz)    -   Sound field simulation of turbulence (>500 Hz)    -   Vibrating the probe in a laminar flow (<1000 Hz)        All methods are difficult and are restricted to low frequencies        Indirect Method “SQUARE WAVE TEST”        By using the indirect method, the sensor is subjected to an        electric sine wave that simulates an instantaneous change in        velocity and analyses the shape of the anemometer output. For a        wire probe (1-order probe response): Frequency limit (−3 dB        damping):        f _(c)=1/1.3 t        Indirect methods are the only ones generally applicable in        practice.        Square wave test determines frequency limits for wire probes.        Time taken by the anemometer to rebalance itself is used as a        measure of its frequency response.        Square wave test is primarily used for checking dynamic        stability of CTA at high velocities.        Indirect methods cannot simulate effect of thermal boundary        layers around sensor (which reduces the frequency response).

A suggested electric circuit to measure the ambient temperature and/orflow velocity is illustrated in FIG. 7. The circuit may be used to findthe variation relationship between E and R_(w) or Voltage drops based onthe constant current source.

Specific Embodiments

In the disclosed embodiments, a fluid flow sensor system includes athermal resistor type of sensor responsive to changes in fluidtemperature and flow velocity. The system is based upon hotwireanemometer technology and provides a thermal transducer mechanism forsensing a known quantity of heat applied to a wire. The rate at whichheat is transferred from the wire is proportional to the difference intemperatures of the sensor wire and of the fluid passing over the wireas a function of fluid velocity. The relationship can be described as:Q=k(T_(sensor)−T_(fluid))·v, where Q is the rate of heat transfer, k isa constant, T sub sensor is the temperature of the sensor, T sub fluidis the temperature of the fluid, and v is the velocity of the fluid.

The heat Q delivered to the sensor is proportional to the square of thecurrent I passing through a wire that has a resistance R, so that:Q=RI².

Using two adjacent thermal resistors at different levels of bias currentwould allow measurement of the two unknowns T_(fluid) and v. In thiscase, heat supplied to one sensor subsystem will transfer to the othersensor subsystem at a rate dependent on the fluid velocity. Thus, onesensor subsystem comprising a first thermal resistor would maintain asufficient temperature differential with the fluid by taking heat fromthe bias current, while the other sensor subsystem comprising a secondthermal resistor approaches and can be virtually at thermal equilibriumwith the fluid. This is the principle by which some mass flowcontrollers control the flow rate. It may also be possible to use onlyone thermal resistance sensor to accomplish the same task by timemultiplexing measurements performed at different bias currents. Thus, asingle sensor acts as both sensor subsystems.

The temperature sensors used for the flow measurement will be based onthe change in the electrical conductivity of a conducting material dueto a change in the ambient temperature. Such a sensor can be calledthermal resistor. It consists of the main resistance with external leadsand auxiliary leads for voltage sensing as illustrated in FIG. 8. Changein the resistance of the main resistor is, to the first orderapproximation, proportional to the change in temperature. To measurechange in the resistance, a small current will be injected through themain resistor leads and voltage will be measured across voltage sensingleads. This method of resistance measurement is known as the “fourpoint” method since four contact points are needed. The advantage ofthis method is that it circumvents the difficulty associated with theeffects of lead and contact resistances, which could dominate theoverall resistance.

The sensor described above also has several advantages over thethermocouple type sensors. For one, thermocouple sensors would requiretwo different metals for its operation. This complicates the sensorfabrication. In addition, the problem of cold junction (or referencejunction) would have to be solved for thermocouple sensors. Lastly, aswill be described below, the measurement of flow and temperaturetogether could be based on regulating the amount of heat produced nextto or by the temperature sensor.

In terms of the described embodiment, a micro-fluidic thermal transducersenses point velocity of fluid flow by measurement of temperaturevariations in a heated resistive wire. A primary resistance withexternal leads and separate auxiliary leads for voltage sensing isemployed, wherein changes in resistance are proportional to changes intemperature. For measurement of change of resistance, a small current isapplied through the primary resistor leads, and voltage is measuredacross voltage sensing leads. Thus, a four-point wire probe measurementmethod is employed, which provides a most accurate reading of desiredtemperature data to the extent that any resistances associated with leadand/or contact resistances are minimized. By the application of a knowncurrent through the wire probe, any changes in voltage are moreaccurately associated with fluidic temperature changes rather than withcontact or lead resistances.

The temperature of the thermal resistor can be obtained from thefollowing relations $\begin{matrix}{{R_{0} = \frac{l}{\omega\quad\tau\quad\sigma_{0}}},} \\{{R = {R_{0} + {\alpha\quad{R_{0}\left( {T - T_{0}} \right)}}}},} \\{V = {V_{0} + {\alpha\quad{V_{0}\left( {T - T_{0}} \right)}I}}}\end{matrix}$where R₀ is the resistance at some reference temperature T₀, σ₀ is theconductivity at the reference temperature, l, ω, τ are the length,width, and thickness of the conducting wires, respectively, l is thebias current, V is the measured voltage, a is the thermo-resistancecoefficient and, finally, T is the sensor temperature.

To appreciate the sensitivity of the proposed thermal resistor it ishelpful to consider some specific numerical values of geometric andphysical quantities in (3). The following list of numerical values willbe assumed for the purpose of estimation:

-   τ=2×10⁻⁴ m, ω=10×10⁻⁴ m, l=25000×10⁻⁴ m, σ₀5×10⁷ 1/Ω·m, α=7000    ppm/C°, l=1 mA

Using the above numbers, the relative change in the voltage signal perdegree Celsius is given by${\frac{\Delta\quad V}{V_{o}} = {\alpha = {7 \times 10^{- 3}}}},$the sensor resistance will be around 25 Ohms and the voltage signalitself is ΔV=2.5×10⁻³ Volts=2.5 mV. This voltage signal is much largerthan the typical thermocouple generated voltage signal. At the sametime, noise coming from the thermal resistor is expected to be only alittle larger than the thermocouple noise. This is due to the fact thatnoise increases as the square root of the wire resistance. Thus, it isexpected that the proposed thermal sensor will have better sensitivitythan a thermocouple.

In the described embodiment, the thermal resistor sensor is constructedof relatively thin layers of dielectric and electrically conductingmaterials having a low thermal mass. The dielectric layers serve assupport and electrical insulation to protect the sensor from theenvironment. The conducting layer is a wire probe that forms the primaryresistance of the sensor, and has leads that share connection junctionswith auxiliary voltage sensing leads that are also connected to theprimary resistance. In one disclosed embodiment, the supportingdielectric layers are formed as a flap that protrudes from the primarygasket body into the coolants or oil fluid aperture where sensing of thefluid is desired. The primary resistor is located on the flap, while allthe leads are extended to areas outside of the gasket to provideelectrical connection therewith.

More specifically, now referring to FIG. 9, an embodiment of a flow ratesensor probe 10 is shown. The probe is deposited on a substrate thatdefines a support body 12 that surrounds a fluid aperture 14. Ascontemplated, the fluid aperture 14 is adapted for the passage of acoolant fluid or an oil through a combustion seal gasket of a vehicle. Afluid sensing wire probe 16 extends partially into the aperture opening,the end 18 of the fluid sensing probe 16 protruding radially into theaperture 14 on a flap 20 that supports the end 18 of the probe in thefluid stream. For purposes of flow sensing, a the fluid flow isorthogonal with respect to the described protrusion of the probe end 18.

Referring now to FIG. 10, a second embodiment of a flow rate sensorprobe apparatus is depicted. The cylinder head gasket 30 includes acombustion aperture 32, a coolant aperture 34, a bolt hole aperture 36,and an oil aperture 28. Normally, there are a plurality of each of theaforedescribed apertures. The gasket 30 has a boundary or extremity 38that is adapted to be fit between an engine block and a cylinder head(neither shown).

A thermal sensing probe 40 is part of a four-point probe hot wireanemometer system employed to detect fluid flow rates through thedepicted coolant aperture 34. The sensing probe 40 extends across andfrom a pair of soldered plates wherein a pair of current supply wires 42are connected to supply a fixed and controlled current through the probe40. In parallel with the wire 42 are a pair of voltage measuring wires44 used to sense changes in voltage. In this manner, the system issensitive to very small temperature changes.

The current and voltage wires 42 and 44 respectively are connected to anengine control unit (ECU) which modulates or controls various enginefunctions as a function of the sensed flow rates being measured, as willbe appreciated by those skilled in the art.

To the extent that the dimensions of the probe 40 are quite small, i.e.on the order of two microns in thickness, a substrate having relativerobustness is required. Normally, a preferred material for the high heatand temperature requirements of an internal combustion engine coolantflow would be a non-conductive material, including materials such as asilicone based material. Circuit printing techniques can be utilized forthe manufacture of such coated wiring. Those skilled in the art willappreciate that screen printing and other circuit manufacturingtechniques can be employed for this purpose.

EXAMPLE

A test fixture 50 is depicted in FIG. 11 for purposes of simulating thehot wire anemometer system of measuring fluid flow.

The test fixture 50 includes a coolant flow aperture 34′ across which isdeposited a thermal sensing probe 40′ as shown. The test fixture has aboundary or extremity 38′ similar to the boundary 38 of the gasket 30described above. In addition, the test fixture 50 incorporates a pair ofsoldered plates 24′, analogous to the plates 24 of the embodiment of thecylinder head gasket 30 of FIG. 2. Also analogously, the current supplywires 42 are directly attached to the soldered plates 24 as described inthe previous embodiment, and share the plates with the voltage measuringwires 44′.

To the extent that the test fixture 50 is not exposed to the harsh heatand temperature environment of an internal combustion engine, i.e., thetest fixture environment was subject only to a temperature of up to 150°centigrade to simulate a hot oil environment, a parylene substrate canbe employed to protect the probe wire 40′.

The Method of Manufacturing A Test Fixture

General Discussion

A Method of manufacturing a test fixture now follows. The material ofchoice for conductivity, particularly in a microfluidic realm wheremeasurements are made in microns of thickness, is copper. To the extentthat the copper layers are quite thin, they are normally commerciallyavailable only with an aluminum backing plate or layer, as purchased forthe manufacture of printed circuit boards. Thus, one micro-fabricationprocess for a gasket flow sensor for the test fixture 50 was completedas described with reference to FIG. 12 which depicts a sequential seriesof steps for the manufacture of a four-point probe hot wire anemometerto be used for measuring fluid flow in the environment described.

In the first step, a commercially purchased preparation of the aluminumand copper layers is depicted as item A of FIG. 12 with the aluminum 60and copper 62 layers shown bonded together. In step B, a protectivesubstrate, non-conductive parylene (a themoplastic film) is shown aslayer 64, juxtaposed against the backside of the copper layer 62, so asto have the copper sandwiched between the aluminum layer 60 and theparylene layer 64.

Next, in step C the aluminum is etched away from the triple layer ofparylene-copper, and aluminum to obtain only a copper-parylenecombination of layers 62 and 64. At this point, a photoresist material66 is applied to the copper side of the parylene-copper structure asshown in step D.

Next, a mask 68 with a desired pattern of the four point anemometerprobe is applied against the photoresist 66. Ultraviolet light, shown asrays 70, is then applied to the photoresist through the mask, which istransparent to the UV light except in those areas of the pattern to berealized on the substrate. The photoresist is pre-baked prior toapplication of the ultraviolet light. After application of theultraviolet the photoresist is post-baked and developed to provide thedesired sensor pattern, shown only representatively.

Finally, the copper is etched away, leaving the sensor pattern of copperon the parylene sheet as shown in Figure G. The post-etch photoresist 72is then removed by conventional techniques, and finally the exposedcopper layers 62′ of the desired pattern, which is typicallydiscontinuous, are then covered with additional parylene so as toachieve the composite shown in sequence I.

Process for Test Sample Sensor

More specifically, test sensors for sensitivity tests could be designedand built by using the following procedure,

-   a. Copper layer of UTC foil was coated by using Parylene deposition    system (PDS). The substrate is aluminum layer.-   b. Aluminum layer can be etched off by the solution of NaOH:DI water    (60 g/1 litter)-   c. Films on dummy silicon wafer are baked on the hot plate at    120° C. for 10 minutes for humid removal.-   d. Spin coat positive Shipley Microposit 1818 at 3500 rpm for 20    seconds for more thickness of photoresist.-   e. Pre-bake the film on the hot plate at 115° C. for 1 minute.-   f. Place the film put on the chuck of mask aligner for exposing the    UV light. Expose for 8 sec with 20 mW intensity. Note that the    thickness of substrate should be checked (Parylene+Copper+Dummy    wafer).-   g. Develop the exposed photoresist using DI water and Microposit 351    developer (=5:1) for 1.1 minute and then Rinse.-   h. Check the sensor pattern using microscope-   i. Rinse and then post-bake the film on the hot plate at 120˜140° C.    for 10 minutes.-   j. Dip the film into the Copper etchant for 15 sec to etch off the    Copper at room temperature and then Rinse-    (Note that ferric chrolide solution was used for copper etching and    the black sludge left on the film surface was removed by soft    touching of clean paper. But, the etching speed of etchant used is    very fast and it makes the etching time hard to control. In practice    it most likely would be desirable to use a weaker etchant like    sodium persulphate. Morover, it would also be desirable to clean the    etchant off quickly and accurately after etching to prevent    overetching and undercut. For removing the aluminum smut, it should    be dipped in a weaker solution containing 50 grams/liter of sodium    persulphate and 3 grams/liter of sulphuric acid for 1 minute. It    should be allowed about 0.1 micron of copper to etch off during the    smut removal for it to be sufficient.)-   k. Remove the photoresist using Microposit 1112A remover and then    Rinse the film.-   l. Wires are needed for soldering to the electrodes for electric    contacts. One concern is that the sensor pattern may be broken due    to the heat of soldering gun. A preferred alternative includes    Silver Epoxy-   m. Coat the side of copper layer with wires by using Parylene    deposition system (PDS).    Batch Process for Sample Sensor-   a. Same as the procedure a to k of previous micro-fabrication    process.-   b. Print the circuit lines or Draw them by using the Etch resist ink    pen on the flexible circuit board.-   c. Etch off the copper on the flexible circuit board-   d. Glue or bond the flow sensor onto the flexible circuit board-   e. Make sure of connecting the circuit lines with the electrodes of    flow sensor using the conductive micro-tip pen.-   f. Coat the side of copper layer and circuit board by using Parylene    deposition system (PDS).-   g. Insert the flexible circuit board with flow sensor between the    gaskets for the Mock-up test    Experimental Tests and Results    Temperature Sensitivity (Calibration) Test—FIG. 13

Sensitivity tests of microfilm sample sensor between temperature andvoltage were carried out. Voltage drops of a microfilm sensor weremeasured by an HP34401, a multi-meter, which is shown in the schematictest setup of FIG. 13. For the calibration purpose of heated watertemperature, a digital thermometer was used. Simultaneously, watertemperature and voltage change of the sample sensor were recorded byhand. A four points measurement method was employed.

Based on the theoretical calculation discussed above, the sensitivitywas 83.85 μV/° C. and determined as follow:The resistance of sensor element is$R_{0} = {\frac{l}{A_{w}\quad\sigma_{0}} = {21.5\quad\Omega}}$

-   -   where, length (l)=25 mm    -   width (w)=10 μm    -   thickness (t)=2 μm    -   A_(w)=w×t    -   ρ_(o)=1.72 μΩm    -   σ_(o)=5.8 e+7 (1/Ωm)    -   α_(o)=3,900 ppm/° C.        Wire resistance can be written as:        R_(w)=R_(o)[1+α_(o)(T_(w)−T_(o))]

To get the limitation of the applied current, the applied current wasincreased monotonically. Under these test conditions, water temperaturewas 21° C. The results are shown in FIG. 14.

From the data set forth in FIG. 14, in order to get the sensitivities oftemperature and flow velocity, it is possible to apply a current valuethat may range from 1 mA to 5 mA. Preferably, 1 mA is selected as anapplied constant current to prevent the wire from burnout.

In constant current mode (I=1 mA), the equation will be rewritten asIR _(w) =IR _(o)[1+α_(o)(T _(w) −T _(o))]=V _(w) =V _(o)[1+α_(o)(T _(w)−T _(o))]=V _(o)+α_(o) V _(o)(T _(w) −T _(o))In case of unit overheat ratio (a≈1), temperature sensitivity of thesensor can be expressed as $\begin{matrix}{S_{\theta,{cc}} = {\frac{\partial E_{w}}{\partial\Theta} = {\frac{\alpha_{0}I{\overset{\_}{R}}_{w}R_{0}}{{\overset{\_}{R}}_{a}} \approx {\alpha_{0}{IR}_{0}}}}} \\{= {{3900e} - {6 \times 21.5 \times 1e} - 3}} \\{= {83.85\quad\left( {µ\quad{V/{^\circ}}\quad{C.}} \right)}}\end{matrix}$Experimental tests were carried out two times with the same film sensorin cases of heating up by hot plate and cooling down in nature. Theresistance of sensor of the sensor was 177.45 Ω and constant currentsource generated 1 mA exactly before test. But, the current was measuredto 0.8420 mA after connecting the wires with the sensor. In here,consider only the resistance of real film sensor (21.5 Ω->177.45 Ω) tomake sense of the experimental sensitivity. It should be influenced fromthe resistance of both electrodes and lengthy wires.S _(θ,cc) ≈α ₀ IR ₀=3900e−6×177.45×0.8429e−3=583.3(μV/° C)

Through the experiments, FIGS. 15 a and b are obtained. It has beenshown in the Figures a and b that the voltage values are linearlyproportional to the water temperature. Approximately, the sensitivity ofthe film sensor was 625 μV/° C. which has 6.7% error compared to thetheoretical calculation.

Flow Velocity Measurement

A. Method I

-   1. In the constant current type, a fine resistance wire carrying a    fixed current is exposed to the flow velocity.-   2. The wire attains an equilibrium temperature when the i²R heat    generated in it is just balanced by the convective heat loss from    its surface.    W=H→I ² ·R _(w) =h·A·(T _(w) −T _(a))→I ² R _(w)=(Nu k _(f) /d)A(T    _(w) −T _(a))    Nu=A ₁ +B ₁ ·Re ^(n) =A ₂ +B ₂ ·U ^(a)    -   “King's law”        I ² ·R _(w) ² =E _(w) ²=(T _(w) −T _(a))(A ₃ +B ₃ ·U ^(n))    -   h=film coefficient of heat transfer    -   A=heat transfer area    -   d=wire diameter    -   T_(w)=wire temperature    -   U=flowing velocity    -   T_(a)=temperature of flowing fluid    -   k_(f)=heat conductivity of fluid    -   Nu=dimensionless heat transfer coefficient    -   A_(i),B_(i)=Calibration constants-    Note: Since the convection film coefficient is a function of flow    velocity, the equilibrium wire temperature is a measure of velocity.    The wire temperature can be measured in terms of its electrical    resistance.-   3. Assume that the measured fluid is at the same temperature and    pressure is fairly simple.-   4. Build circuit as shown in FIG. 16.-   5. In calibration, flowing velocity U is set at known value U₁. Then    R_(I) is adjusted to set the current I at a value low enough to    prevent wire burnout but high enough to give adequate sensitivity to    velocity.-   6. The resistance R_(w) will come to a definite temperature and    resistance. i.e., meter deflection indicates the resistance change    of the bridge circuit (e_(AC)≠0, deflection method).-   7. Then R₃ is adjusted to balance the bridge (e_(AC)=0 based on the    relation of R_(l)/R_(w)=R₂/R₃, null method). This adjustment is    essentially a measurement of wire temperature, which is held fixed    at all velocities (=constant temperature).-   8. Plot I₁ ² and U₁ ^(1/2).-   9. Flowing velocity U is changed to a new value, causing the wire    temperature and R_(w) to change thus unbalancing the bridge.-   10. R_(w), and thus wire temperature, is restored to its original    value in step 6 by adjusting the current I (by means of R_(I)) until    the bridge balance is restored (R₃ is not changed).-   11. The new current I and the corresponding flowing velocity U may    be plotted on the calibration curve with axis of I² and U^(1/2) and    this procedure is repeated for the many velocities as desired.    B. Method II—FIG. 17-   1. Using 4-points measurement.-   2. Applied constant currents, which ranged from 0 to 10 mA to    prevent the sensors from burning out.-   3. The output voltage is obtained by measuring the voltage drop    across the probe sensor. This circuit can be used for steady-state    measurements.    Flow Sensitivity Test (Calibration Test)

Based on Method II above, flow sensor evaluation and testing werecarried out in order to obtain the sensitivity of the sample flowsensor. The test setup schematic is shown in FIG. 18. The sensor wasinstalled between two steel plates with gaskets and hooked up thedigital meter (Instek: DM8055) and constant current power supply. Tocalibrate the sample sensor, LU-05609 flow sensor manufactured by ColeParmer was installed.

Test Results

1. Current vs. Resistance (No Flow)

-   a. 0 to 5 mA—FIG. 19

Current(mA) Resistance(Ω) 0 221.81 1 351.84 2 490.73 3 639.46 4 799.29 5971.63

-   b. 5 to 10 mA—FIG. 20

Current(mA) Resistance(Ω) 0 215.39 5 936.44 6 1114.36 7 1308.24 81518.65 9 1748.62 10 2001.5

Constant currents were applied to the sample sensor with no flowcondition in order to check the burnout of the sample sensor up to 10mA. There was no burnout with 10 mA and also current applied waslinearly proportional to the resistance of a sample sensor as expected.With flow of the coolant, currents of 1 mA, 5 mA, and 10 mA wereapplied, respectively. With 1 mA, good results were not achieved. Thismay come from the fact that test sensor required more heat generationsto have good heat transfer to the flow. That's one of the reasons whythe applied currents were increased.

2. Flow Rate vs. Voltage Drop

Test I: flow test (5 mA)—FIG. 21

Test I: flow test (5 mA) - FIG. 21 Flow rate(G/m) Voltage drop(VDC) 00.7069 20.7 0.6991 24.7 0.69751 25.8 0.69503 0 0.69697 20.3 0.6885 24.70.68793 0 0.69134Test II: flow test (5 mA)—FIG. 22

Flow rate(G/m) Voltage drop(VDC) 0 0.66594 19.2 0.65021 21.4 0.6489 25.40.65069 0 0.65431Test III: flow test (10 mA)—FIG. 23

Flow rate(G/m) Voltage drop(VDC) 0 1.32838 11.2 1.31805 12.3 1.3180517.7 1.31578 19.2 1.31398 19.6 1.31325 20.7 1.31162 22.1 1.31009 22.81.30963 23.2 1.30907 23.6 1.30858 24 1.30827 24.3 1.30632 24.7 1.3059525 1.30535 25.4 1.30486 25.8 1.30428 25 1.30584 24 1.30647 23.6 1.306722.5 1.30684 20.7 1.307 14.7 1.30734 0 1.31563

-   1) Through the test results above, the sensitivity of a sample flow    sensor can be approximately estimated, ˜1 mV/Gal/min. This value is    not exact and well not approximated. There are many uncertainties    that resulted from the extrusion-type design of a micro sample    sensor and non-steady-state (irregular) flows in pipe due to various    diameter changes of test setup and not enough distances between the    valve and sensors.-   2) An extrusion type sensor may not have enough strength to resist    the high velocity flows so that it would be deflected and flipped    during measurement. Therefore, preferably this kind of flexible    sensor design should be modified and enhanced into the design of the    cross-hole type sensor in order to guarantee the robustness of flow    measurement.-   3) There was hysteresis between voltage drop and flow rate signals,    possibly due both to irregular flows nearby the sample sensor as    well as instrumentation limitations.-   4) To obtain the regular flow (steady state flow), flow control    valve should be used for controlling the coolant flow and it should    be positioned to have enough distance from the sample sensor.-   5) Flow sensor (LU-05609) seems to have low dynamic response, which    may be due to manually controlled valve. It also cannot measure the    low range of flow rate 0 to 18 Gal/min, which may be due to not    enough flow to rotate the turbine or low resolutions.

In summary, from a standpoint of testing, fluid velocity and fluidtemperatures were calibrated separately. Through the measurement offluid (water) temperature, voltage drops were linearly proportional tothe fluid temperature. The sensitivity of the sample sensor was 625 μV/°C. To get this value 1 mA constant currents were applied to the samesample sensor with no flow condition. To check the burnout of a samplesensor, constant currents were applied up to 10 mA. No burnout was foundof a sample sensor with 10 mA. The applied currents were linearlyproportional to the resistance of the sample sensor with no flows.

For the flow rate calibration, testing tried to measure the flow rate orflow velocity with currents of 5 mA and 10 mA, respectively. Currents of1 mA were also tried, but the results were not desirable.

From the test results, it is possible to approximate the sensitivity ofa sample flow sensor, 1 mV/Gal/min. However, there were manyuncertainties that resulted from the extrusion type design of the microsensor and the non-steady-state (irregular) flows in the pipe due tovarious diameter changes of the test setup and the lack of sufficientdistance between the valve and the sensors. Therefore, it is preferredthat a cross-hole type sensor be used under appropriate circumstances tohave sufficient strength for resistance to high velocity flows withoutdeflection or flipping, and that the distance between the valve andsensors be adjusted.

It is to be understood that the above description is intended to beillustrative and not limiting. Many embodiments will be apparent tothose of skill in the art upon reading the above description. Therefore,the scope of the invention should be determined, not with reference tothe above description, but instead with reference to the appendedclaims, along with the full scope of equivalents to which such claimsare entitled.

1. An apparatus comprising a gasket adapted for insertion between matedsurfaces for sealing therebetween, said gasket comprising: at least oneaperture with an edge for accommodating a flow of fluid therethrough; atleast one sensor responsive to temperature for sensing heat transferindicia, wherein said sensor extends partially into said fluid apertureof said gasket and away from said edge so as to be in direct contactwith fluid passing through the fluid aperture.
 2. An apparatus asrecited in claim 1, wherein said sensor comprises an anemometer device.3. An apparatus as recited in claim 1, wherein said gasket is subjectedto a range of temperatures including ambient temperature and an elevatedoperational temperature.
 4. A sensor for use in a multi-layer gasketincluding at least one aperture having an edge and accommodating a flowof fluid and varying temperatures and pressures, said sensor extendingpartially into said aperture such that said sensor is capable of beingin direct contact with the flow of fluid.
 5. A sensor as recited inclaim 4 including a thermal resistor.
 6. A sensor as recited in claim 5,wherein said sensor is a hotwire anemometer probe including a thermaltransducer mechanism for sensing a known quantity of heat applied to awire.
 7. A sensor as recited in claim 5, wherein a single thermalresistor sensor uses multiplexing measurements at different biascurrents to comprise first and second sensor subsystems.
 8. A sensor foruse in a multi-layer gasket including: at least one aperture having anedge and accommodating a flow of fluid and varying temperature andpressures; said sensor extending partially into said aperture; whereinsaid sensor includes two sensor subsystems with adjacent thermalresistors at different levels of bias current to allow measurement ofthird temperature and fluid velocity.
 9. A sensor subsystem as recitedin claim 8, wherein a first sensor subsystem with a first thermalresistor maintains a sufficient temperature differential with a flowingfluid by taking heat from said bias current.
 10. A sensor as recited inclaim 8, wherein a second sensor subsystem with a second thermalresistor approaches thermal equilibrium with a flowing fluid.
 11. Asensor as recited in claim 10, wherein heat supplied to one of saidthermal subsystems is transferred to the other of said thermalsubsystems at a rate dependent on fluid velocity.
 12. A sensor for usein a multi-layer gasket including: at least one aperture having an edgeand accommodating a flow of fluid and varying temperatures andpressures; wherein said sensor extends partially into said aperture;wherein said sensor further includes a thermal resistor that is based ona change in electrical conducting material due to a change in ambienttemperature.
 13. A sensor as recited in claim 12, wherein said sensorcomprises a patterned metallic layer embedded within a non-conductivematerial.
 14. A sensor as recited in claim 13, wherein said metalliclayer includes copper and said non-conductive material includes athermoplastic film.